Immune response to an epitope of the NS4 protein of hepatitis C virus in HCV-related disorders

Evaluation of core and NS4B synthetic peptide-based immunoassays for the detection of hepatitis C virus antibodies in clinical samples from Cameroon, Central Africa

BACKGROUND

According to previous data, the antibodies produced during natural hepatitis C virus (HCV) infection frequently recognize amino acids 10-43 in the core protein and 1689-1740 or 1921-1940 in the non-structural 4B (NS4B) protein. The reactivity of these peptides with the corresponding antibodies has mainly been evaluated using serum samples from Western countries where HCV genotype 1 (HCV-1) is predominant, and no information is available concerning samples from sub-Saharan countries where high HCV variability has been reported. OBJECTIVE OF THIS STUDY: To evaluate the performance of HCV core and NS4B peptide-based immunoassays in the serodiagnosis of HCV infection in Cameroon subjects.

STUDY DESIGN

Three core and four NS4B-based synthetic peptides derived from HCV genotypes 1b and 2a were designed and tested against a panel of 151 serum samples from Cameroon (40 positive for HCV-1, 32 for HCV-2, 39 HCV-4, and 40 HCV-negative).

RESULTS

The three core peptides all demonstrated strong immunoreactivity, regardless of the HCV genotype from which they were derived, with greater than 90% and 92% sensitivity and specificity. In contrast, the NS4B-derived peptides exhibited lower sensitivities (24.3-65.8% depending on the HCV genotype) but higher specificities (100% for all four peptides tested).

CONCLUSIONS

Our findings indicate that an HCV core peptide could be used for the diagnosis of chronic HCV infection. Among the NS4B peptides tested, a chimeric NS4B peptide encompassing both N- and C-terminal portions of the NS4B protein gave a much better performance than the two component N- and C-terminal peptides used individually.

Mixed cryoglobulinemia

Mixed cryoglobulinemia (MC), type II and type III, refers to the presence of circulating cryoprecipitable immune complexes in the serum and manifests clinically by a classical triad of purpura, weakness and arthralgias. It is considered to be a rare disorder, but its true prevalence remains unknown. The disease is more common in Southern Europe than in Northern Europe or Northern America. The prevalence of 'essential' MC is reported as approximately 1:100,000 (with a female-to-male ratio 3:1), but this term is now used to refer to a minority of MC patients only. MC is characterized by variable organ involvement including skin lesions (orthostatic purpura, ulcers), chronic hepatitis, membranoproliferative glomerulonephritis, peripheral neuropathy, diffuse vasculitis, and, less frequently, interstitial lung involvement and endocrine disorders. Some patients may develop lymphatic and hepatic malignancies, usually as a late complication. MC may be associated with numerous infectious or immunological diseases. When isolated, MC may represent a distinct disease, the so-called 'essential' MC. The etiopathogenesis of MC is not completely understood. Hepatitis C virus (HCV) infection is suggested to play a causative role, with the contribution of genetic and/or environmental factors. Moreover, MC may be associated with other infectious agents or immunological disorders, such as human immunodeficiency virus (HIV) infection or primary Sjögren's syndrome. Diagnosis is based on clinical and laboratory findings. Circulating mixed cryoglobulins, low C4 levels and orthostatic skin purpura are the hallmarks of the disease. Leukocytoclastic vasculitis involving medium- and, more often, small-sized blood vessels is the typical pathological finding, easily detectable by means of skin biopsy of recent vasculitic lesions. Differential diagnoses include a wide range of systemic, infectious and neoplastic disorders, mainly autoimmune hepatitis, Sjögren's syndrome, polyarthritis, and B-cell lymphomas. The first-line treatment of MC should focus on eradication of HCV by combined interferon-ribavirin treatment. Pathogenetic treatments (immunosuppressors, corticosteroids, and/or plasmapheresis) should be tailored to each patient according to the progression and severity of the clinical manifestations. Long-term monitoring is recommended in all MC patients to assure timely diagnosis and treatment of the life-threatening complications. The overall prognosis is poorer in patients with renal disease, liver failure, lymphoproliferative disease and malignancies.

The IgG antibody profile to various antigen regions of hepatitis C virus differs in oral fluid and serum of patients with chronic hepatitis C

Antibodies to hepatitis C virus (HCV) can be detected not only in serum but also in oral fluid. The aim of the study was to determine IgG antibody reactivity directed to six antigen regions of HCV in oral fluid and to evaluate the significance of the antibody pattern in oral fluid compared to serum. Oral fluid and serum samples of 32 HCV viremic patients were collected to detect antibodies to six antigen regions incorporated as antigen bands into modified commercial updated third generation line immuno-assay. Compared to serum, a significantly lower cumulative antibody response and reactivity to five HCV antigens was found in oral fluid. The significantly highest prevalence of oral fluid reactivity was recorded with antigen C1 (78%), whereas in serum the most significantly frequent reactivity was detected with antigen NS3 (100%). The absence of antibody reactivity with antigen E2 was similar in both body fluids. The discrepancy in antibody pattern to HCV antigens between oral fluid and serum indicates the possible existence of local viral replication, viral mutants, viral inhibitors in oral cavity and, most probably, leakage of the muco-vascular barrier.

Peptide arrays for highly sensitive and specific antibody-binding fluorescence assays

We report a novel generation of peptide arrays fabricated by site-specific ligation of glyoxylyl peptides onto glass slides covered by a semicarbazide sol-gel layer. These arrays allowed the highly sensitive and specific detection of antibodies in very small blood samples from infected individuals using three model peptidic epitopes (HCV Core and NS4, EBV Capsid) in an immunofluorescence assay. Comparison with standard enzyme-linked immunosorbent assays (ELISAs) demonstrated a large gain in sensitivity and specificity. These unique properties, combined with the possibility to immobilize glycoproteins such as antibodies, offer the possibility to perform sandwich immunofluorescent assays in a highly parallel format.

Restricted isotypic antibody reactivity to hepatitis C virus synthetic peptides in immunocompromised patients

An enzyme immunoassay based on three synthetic peptides from the core, NS4, and NS5 regions of hepatitis C virus allowed the detection of antibodies in 100% of immunocompetent infected patients and in 91% of immunocompromised patients (hemodialysis and hemophiliac patients). Immune impairment seemed to restrict the spectrum of antibody isotypes reacting to the core peptide.